Class A Aircraft - Take-off — Page 379, Lesson 467

Let’s pick this up right where the factors affecting V1 begin to multiply. We’ve already seen how mass and aeroplane configuration influence V1 — now I want to walk you through the remaining three factors: density, runway slope, and wind. First, configuration. The next factor to affect V1 is the aeroplane configuration. Page 18 lists the V speeds for 5 degrees of flap, and page 19 lists the V speeds with 15 degrees of flap. So comparing the speeds from these two pages tells us the effect of the flaps. On page 18, which is 5 degrees of flap, using column A again, a 55,000 kg mass requires a V1 speed of 137 knots. But on page 19, which is 15 degrees of flap, for the same mass of 55,000 kg, the V1 speed is now 130 knots. Therefore, we can see that increasing the flap angle decreases V1. That’s a direct, clean relationship — more flap, lower V1. Now density. The next factor to affect V1 is density, but this is a little harder to observe than the previous two factors. On page 17 of section 4 there’s a small table with temperature on one axis and pressure altitude on the other. This is the density accountability table. Under low altitudes and low temperatures is band A. This is a high density band, whereas band F is situated at higher temperatures and higher altitudes, which equates to much lower densities. So the bands run from A — high density — down to F — low density. We can now use these bands to see the effect density has on V1. Returning to page 18, notice that bands A, B, C, D, E and F are in the speed tables. Taking a mass of 50,000 kg in band A, which is high density, V1 is 129 knots. But in bands B, C, D and E, the value of V1 is increasing. Therefore, as density falls — shown by going through bands A to E — V1 increases. So lower density means higher V1. Finally, slope and wind. The last two factors that affect V1 are runway slope and wind. Notice that at the top of pages 18 and 19 there is a table titled “Slope and Wind V1 adjustment.” If there were a downslope of 2%, then with an aeroplane mass of 70,000 kg, V1 would have to be reduced by 3 knots. So a downslope — the runway sloping downward — reduces V1 by that adjustment amount. And wind, of course, is the other factor in that same adjustment table, though the excerpt cuts off right there. So to summarise the full picture: mass increases V1, increasing flap angle decreases V1, falling density increases V1, and a downslope reduces V1 by the tabulated adjustment. Each of these is a distinct input you’ll need to account for when you compute V1 for a real take-off.